First time using a vacuum bleeder (harbor freight mity-vac style) on my SMT with ABS.

I found the recommendation for thread sealing after the fact. I just did the rear but so much air was being pulled through the threads that I had to pump the vacuum pump constantly. The fluid would just sputter through the tube. I couldn't judge its color so I stopped after about 2.5 oz.

Did I just introduce air into the system?

So I can use the normal white PTFE tape sold in the plumbing dept?

What's going to happen when I remove the bleeder screw to apply the tape? Much fluid loss? Should the reservoir cap be on or off?

Not likely you added air. When it comes to using a vacuum bleeder you need to make sure the threads are clean, and barely crack open the bleeder to minimize pulling air past the threads so you can see how well you are doing. Personally I don't use a bleeder unless I have a bubble I can't force through with conventional bleeding.

I've used the Mity-Vac, but with pressure - bleeding clutches from below pushing fluid up to the master from the slave.
Worked great on my FJ1200, and on a Ford Ranger (it's impossible to bleed a Ranger clutch effectively any other way).
I had no problem with the threads when using pressure.

Brake bleeder screw works more like a needle/seat in a carb. The threads don't seal. The screw has a tapered seat that seals against the slave cyl.
If there was no air in the system before you started it's probably okay. I've bled lots of brakes with a vac bleeder with lots of bubbles coming out of the nipple. No problemo.
If you want to see what's coming out, use the coke bottle method. A clear bottle with a little fresh brake fluid in it. Be sure the drain hose stays submerged in the bottle of fluid & watch what comes out. Keep pumping until it runs clear.

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Not likely you added air. When it comes to using a vacuum bleeder you need to make sure the threads are clean, and barely crack open the bleeder to minimize pulling air past the threads so you can see how well you are doing. Personally I don't use a bleeder unless I have a bubble I can't force through with conventional bleeding.

1) Teflon tape will seal the bleeder screw threads, but as Jim said, not recommended.
2) Barely squeeze the lever/pedal while applying vacuum at the just-cracked bleeder screw. Pressure from above and vacuum below tends to move things along nicely.
3) Doubtful you added air in the system.

I'd never seen a gizmo like this before, bled brakes before, or swapped brake fluid before. Had the whole job done in 15 minutes with only a little drippage from the screw, and that was solved with a paper towel. An extra foot of 3/16" tubing comes in quite handy, though, as the included tubing isn't long enough to reach a container. Three pumps of the lever primed the unit and I was off to the races. Remember to check the master cylinder fluid level and top up as needed.

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Not likely you added air. When it comes to using a vacuum bleeder you need to make sure the threads are clean, and barely crack open the bleeder to minimize pulling air past the threads so you can see how well you are doing. Personally I don't use a bleeder unless I have a bubble I can't force through with conventional bleeding.

I would not recommend any kind of tape on the threads.

Jim

I tried opening from a little to a lot. At the smallest setting it just didn't pull very much fluid through before I lost nearly all the vacuum. I'll see how the brake feels tomorrow before attempting the fronts.

I should raise the catch bottle above the level the caliper as this should allow fluid accumulate in the hose.

I ran into the same thing using a Mityvac, air is sucked in through the bleeder threads but then goes right back out the bleeder nipple...makes it impossible to visually tell when all the air is out of the system like when bleeding brakes the traditional way but it DID work when I ran enough fluid through, the brake pedal was high and firm...in my case I was working on a car w/ two master cylinders and a balance bar so the traditional method was useless. One trick I've read about is to use ATE blue brake fluid every other flush/bleed so you can tell when all the old fluid is gone but on most vehicles I've worked on the old fluid is dark enough with age that it is obvious when the new fluid is coming out the bleeder.

In nearly 40 years of bleeding brakes, I've used tape, grease, pipe dope or nickel anti-seize when needed.

Using tape can allow some tape to get into the brake lines and block the very small valves. Pipe dope can do the same. Grease is likely going to desolve in the fluid, but I prefer pure brake fluid only in the system.

I use a syringe I copped at a farm & Fleet like place, designed for vets (no needle) . . . . pop the right sized tubing on the the business end, fill with fluid, put the tubing on the fitting, crack it, and push the fluid up.

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